Signal generator



March 5, 1935. G. L. BEERS SIGNAL GENERATOR Filed March 1o, 1952 Patented Mar. 5, 1935 UNITEDV s'rarlzs PATENT OFFICE SIGNAL GENERATOR George L. Beers, Collingswood, N. J., assigner to Radio Corporation of America, a. corporation of Delaware Application March 10, 1932, Serial No. 597,926

2 Claims.

My invention relates to signal generators and,

more particularly, to the modulation and control of signal generators adapted to op high radio frequencies.

vWhen an attempt is made to directly modulate erate atl ultra an lultra high frequency oscillator by conventional methods, a certain amount shift occurs.

of frequency- The frequency shift is detrimental to eflicient reception of the signals in the event that the oscillations are transmitted toremotely disposed, sharply tuned receivers.

Furthermore, a source of modulated oscillations, at'ultra high frequency, is required for the testing o-f certain radio apparatus and for other purposes well known to those skilled in the art. Here, again, constancy of frequency is desirable.

Furthermore, in testing radio apparatus, it is necessary vthat means shall be provided whereby the modulated oscillations may be attenuated, by

known steps, in order to calibrate t ratus as to sensitivity, selectivity, etc.

he said appa- Those skilled in the art appreciate the diiiiculty in satisfactorily attenuating oscillations at ultra high frequencies by conventional methods.

It is,-accordingly, an object of my invention to provide a stable sourceY of modulated high frequency oscillations.

Another object of my invention is to provide a system for the production of modulated ultra high frequency oscillations wherein frequency shift, occasioned by the modulation,

is minimized.

A further, and more specific object of my invention, is to provide means whereby oscillations at ultra high frequencies may be attenuated to known values for testing apparatus.

The foregoing objects, and other objects appurtenant thereto, I accomplish, in a preferred embodiment of my invention, through the utilization of a plurality of oscillators.

One oscillator is adjusted to a relatively low frequency, and is controlled by a modulating device.

The output from another oscillator, at a relatively high frequency, and the output from the modulated oscillator are simultaneously impressed upon a rectifying device, with the result that a beat frequency output current is produced that carries the modulation frequencies.

obtained in one or two steps.

Theoretically,

however, no limit is imposed upon the number of steps and my invention is not to be considered as in any way restricted by the herein-described preferred embodiment.

The novel features tha I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment, when read connection with the accompanying drawing, in which Fig. l is a simplified diagrammatic wiring diagram of a signal generator including a preferred embodiment of my invention;

Fig. 2 is a similar diagram of a modification, and

Fig. 3 shows diagrammatically still another modification.

Referring to the drawing, a signal generator constructed according to my invention preferably includes a relatively low frequency oscillator 1, and a relatively high frequency oscillator 3. The oscillation frequencies are so chosen that the sum or difference frequency is the desired high frequency or is a frequency materially higher than that of the low frequency oscillator. For example, if the high frequency desired is 6 megacycles, the low frequency oscillator may be tuned to one megacycle and the relatively high frequency oscillator, which may be crystal-controlled, may be tuned to 5 or 7 megacycles.

' The low-frequency oscillator, preferably, though not necessarily, is constituted by a thermionic tube 5 of the four-electrode type, having a cathode 7, a plurality of grids 9 and l1, and an anode 13. If one of the grids is utilized as an anode and the other provided with a tuned input circuit 15, the oscillation frequency is not materially affected by conditions in an output network 15 connected between the anode and the cathode. A modulator 17 is connected in shunt relation to the said output circuit in the well known manner ascribed to Heising and any desired signal source 18 may be associated with the said modulator.

Naturally, other well known modulation networks may be employed, if desired.

The radio-frequency output circuits 19 and 2l,

respectively, of the high and low frequency oscillators are coupled to input circuits 23 and 24 of a rectifying device 25. In the drawing, the said device has been indicated as being of the fourelectrode type, having a plurality of grids 27 and 29, biased as for rectification, a cathode, 31, and an anode 33. If the two grids are utilized as input electrodes for the high and low frequency oscillations, respectively, coupling between the oscillators themselves is minimized. A shield 35 may also be provided. Any other rectifier may be utilized, however, with good results as, for example, the balanced system shown in Fig. 2, wherein elements analogous to those shown in Fig. 1 are designated and hereinafter referred to.

An adjustable attenuator 37 may be interposed between the modulated oscillator and the rectifier input, if the output from the rectifier is to be calibrated and made use of for measuring purposes. In such event, of course, the rectifier should be linear.

The attenuator, since it functions at a relatively low frequency, may be quite simple in construction, and conventional in type.

The rectier is provided with an output circuit 39 tuned to the beat frequency which, in the example given, is 6 megacycles. Modulated oscillations at the said frequency, appearing in the output circuit, may be utilized in any desired manner although, if a still higher frequency is necessary, perhaps for radio or television transmission, the process may be repeated.

Referring now to Fig. 2, adjustable attenuator 38 may be interposed between a modulated oscillator 14 and the input coupling transformer 22-30.

The rectifier is provided with a high frequency input circuit 26-28 coupled to the high frequency output circuit 20 and with an output circuit 40 tuned to the beat frequency which, in the example given, is 6 megacycles. Modulated oscillations at the said frequency, appearing in the output circuit are passed through the coupling system indicated at 42 and may be utilized in any desired manner.

Assuming, for example, that a radiation frequency of 60 megacycles is desired, the oscillations at 6 megacycles may be passed through an appropriate filter, or coupling system 41, and impressed upon an amplifier 43. The output from the amplifier, together with the output from a 54 or 66 megacycle oscillator 45, may then be impressed upon a rectifier 47 to produce a beat frequency of 60 megacycles which still carries the modulation frequencies. Obviously, the beat frequency may be utilized at this point, if of suicient amplitude, or it may be amplified in a suitable amplifier 49 before utilization.

It should, of course, be kept in mind, as hereinbefore stated, that the desired ultra-high frequency may be obtained in a single step, provided the difference between the beat-frequency and that of the igh-frequency oscillator is sufficiently great to permit of adequate separation by means of filters.

The advantages attending the practice of my invention should now be apparent. By modulating an oscillator at a relatively low frequency, the absolute frequency-shift is comparatively small. When the modulated output of the low frequency oscillator is combined with that from a high frequency oscillator, the frequency-shift with modulation, of the resultant beat-frequency, is very much less than vif the high-frequency oscillator were modulated `directly in the usual manner.

My invention, also, is of value in the event that a modulated signal source, having` high stability yet capable of frequency adjustment within a limited range, is required. For such purpose, I prefer to apply crystal control to the high frequency oscillator as indicated at 4 in Fig. 1 for example, and to provide means such as the condenser 2 whereby the frequency of the low frequency oscillator, as Well as the tuning of the rectifier output circuit and the filter circuits may, simultaneously, be altered to cover the specified range as by condenser 12.

In addition, my invention is applicable as shown in Fig. 3 to superheterodyne radio receivers operating at ultra-high frequencies where high selectivity is essential, for the purpose of supplying the locally generated oscillations. In such case, the modulator, naturally, is omitted, and the unmodulated output from the system indicated at 50-51-52 is caused to beat with an incoming carrier frequency in the manner of two signals in the detector 25 of Fig. l. A detector of this type is shown in Fig. 3 at 53, receiving the signal from an input circuit 54 and the oscillator frequency through input circuit 55. The output circuit is indicated at 56.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In a signal generator, a source of modulated low frequency oscillations including an electric discharge amplifier device having two grid elements and an anode, a tuned input circuit connected with one of said grids,` means for utilizing the other of said grids as an anode in association with the first named grid to produce oscillations, a tuned output network connected with the anode, a modulator means connected with said output network, a source of unmodulated high frequency oscillations having a tuned output circuit, an electric discharge rectifier device, a pair of separate input circuits for saiddevice, one of said input circuits being coupled to the output circuit of the high frequency oscillator and the other of said input circuits being coupled to the output network of thelow frequency oscillator, said device having a pair of control grid elements each connected with one of said input circuits, and a tuned output circuit for said rectifier device.

2. In a signaling system, a high frequency S- cillator, means for maintaining the oscillations therein substantially constant in frequency, an electron discharge device having a. cathode, an anode and two grids biased as for rectification. a tuned input circuit connected to each 0f Said grids respectively, means for coupling said oscillator to one of said input circuits, a second electron discharge device having means including a cathode and two grids for generating low fre quency oscillations, said second electron discharge device having a tuned output circuit including an anode, means fory impressing modulations upon said output circuit, coupling means for transferring modulated low frequency potentials from said output circuit to that one of the grids of the first named electron discharge device whichy is independent of said high frequency oscillator, and a tuned output circuit including the anode of the first named electron discharge device.

GEORGE L. BEERS. 

